The subject matter disclosed herein relates generally to power converters, and more specifically, to clamp circuits for transistor switches in power converters.
At least some known power converters utilize switching circuits including transistors capable of handling high currents and voltages. Rapidly switching the transistors on and off in such circuits is beneficial to the quality of the power output of the converter. Due to the charging and/or discharging of the switching circuit during transient operating conditions (i.e., while turning on and off the transistors), switching losses are induced. To reduce switching losses and improve power output, it is beneficial to maintain a relatively high voltage at collector terminals of the transistors.
Transistors in at last some known power converters have operating limits, which, if exceeded, may damage the transistor and/or other components in the power converter. Accordingly, to operate transistors within an acceptable range, at least some known power converters utilize a voltage clamp circuit, such that if the voltage at the collector terminal exceeds a certain amount, the voltage clamp circuit limits a peak voltage between the collector terminal and the emitter terminal of the transistor. Due to part-to-part variation and temperature variation, however, at least some known voltage clamp circuits have a relatively wide range of operation. That is, the precise voltage at which the voltage clamp circuit will shut off the switching circuit may vary significantly depending on the components in the voltage clamp circuit and the temperature of those components. Accordingly, in at least some known switching circuits, to avoid risking operation of the transistor above the operating limits, the switching circuit must be operated at voltage levels substantially below the operating limits, increasing turn off losses and reducing power output of the converter.